The present invention refers to internal combustion engines of the type comprising a pair of camshafts for driving engine valves, a transmission connecting the driving shaft to a first of said camshafts and a transmission connecting respective end portions of the two camshafts therebetween.
In the engines of the type indicated above, the transmission connecting the two camshafts may for example be a gear transmission, or a chain transmission, or a toothed belt. The gear transmission practically cannot be used in cases where the distance between the axes of the two camshafts is greater than the limit value, beyond which the overall dimension and weight of the gear transmission exceed the limit. The toothed belt is simple and inexpensive but the life thereof is considerably lower than that of the engine, and of the motor vehicle on which the engine is mounted, hence it implies one or more belt replacement operations during the life of the motor vehicle. The chain transmission, lastly, requires a hydraulic belt tensioning device, which requires additional weight and cost, it is subjected to clearances, it is noisy and also, though lasting longer than a toothed belt it is still subject to limits even from this point of view.